1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a transflective liquid crystal display device which includes both of a transmissive region and a reflective region in each pixel region, and a manufacturing method thereof.
2. Description of Related Art
As a liquid crystal display device, there have been known a reflective liquid crystal display device, a transmissive liquid crystal display device, and a transflective liquid crystal display device which is the combination of the reflective liquid crystal display device and the transmissive liquid crystal display device. The transflective liquid crystal display device forms both of a transmissive region which allows light from a backlight to pass therethrough and a reflective region which reflects an external light in each pixel region thus realizing advantages of the transmissive liquid crystal display device and the reflective liquid crystal display device by one liquid crystal display device.
As a type of transflective liquid crystal display device, there has been known a transflective liquid crystal display device which includes incorporated diffusion plates (inner-surface diffusion reflection plates). The incorporated diffusion plate includes a metal film which diffuses and reflects an external light incident from a display screen side in the direction toward the display screen in a reflective region of each one pixel on an inner surface of the substrate. FIG. 11 is a schematic plan view for explaining a constitutional example of one color pixel of the transflective liquid crystal display device. A color pixel CP is constituted of three pixels (also referred to as sub pixels) R, G, B forming a trio. The respective pixels R, G, B are defined by a black matrix BM, wherein the pixel R includes a reflective portion RR and a transmissive portion TR, the pixel G includes a reflective portion RG and a transmissive portion TG, and the pixel B includes a reflective portion RB and a transmissive portion TB.
A size in the lateral direction (a size in the gate-line direction) of the reflective portions RR, RG, RB is indicated by PH and a size in the longitudinal direction (a size in the data-line direction) of the reflective portions RR, RG, RB is indicated by PV. A size in the lateral direction of the transmissive portions TR, TG, TB is indicated by PH and a size in the longitudinal direction of the transmissive portions TR, TG, TB is indicated by TV. A size in the lateral direction of the color pixel CP is indicated by PH and a size in the longitudinal direction of the color pixel CP is indicated by PV.
FIG. 12 is a cross-sectional view taken along a line A-A′ in FIG. 11 for explaining a constitutional example of a transflective liquid crystal display device. In FIG. 12, the transmissive portions TR, TG, TB shown in FIG. 11 are collectively indicated as a transmissive region TA, and the reflective portions RR, RG, RB shown in FIG. 11 are collectively indicated as a reflective region RA. In FIG. 12, a thin film transistor TFT is formed on an inner surface of a TFT substrate SUB1 which constitutes a first substrate. The thin film transistor TFT is formed of a gate electrode GT, a gate insulation film GI, a silicon semiconductor layer (not shown in the drawing), a source electrode (drain electrode) SD1, and a drain electrode (source electrode) SD2.
A protective film PAS which is preferably made of a transparent insulating material is formed in a state that the protective film PAS covers thin film transistors TFT, and pixel electrodes PX formed of a transparent conductive film which is preferably made of ITO are formed on the protective film PAS. The pixel electrode PX is connected to the source electrode (drain electrode) SD1 via a contact hole CH formed in the protective film PAS, and is driven by the thin film transistor TFT. In such a constitution, a film thickness of the protective film PAS is small in the transmissive region TA and is large in the reflective region RA. On a surface of the protective film PAS in the reflective region RA, a diffusion reflective electrode MT having an uneven surface which is formed of a sputtered metal film is formed. A cell gap g1 in the transmissive region TA is set to a value twice as large as a cell gap g2 in the reflective region RA so as to make optical phases of transmissive light and reflection light agree with each other. As a constitutional example in which a resin-made coating film containing particles therein is used and a diameter of the particles is set larger than a film thickness of a coated film thus allowing the particles to project from the coating film to form an unevenness of a background layer of a diffusion reflective electrode on a surface thereof, a technique disclosed in patent document 1 can be named.
On the other hand, on an inner surface of a color filter substrate (CF substrate) SUB2 which constitutes a second substrate, color filters CF which are defined by a black matrix BM, an overcoat layer OC and counter electrode (common electrodes) AT are formed. Here, although an orientation film is formed on an interface between the TFT substrate and a liquid crystal layer, such orientation layers are omitted from the drawings.
Further, the orientation of liquid crystal is disturbed by a stepped portion between the transmissive portion TA and the reflective portion RA and leaking of light occurs in performing a black display. Here, the black matrix BM is provided between the neighboring pixels and hence, the black matrix BM constitutes a non-transmissive portion NT whereby the leaking of light does not occur. However, the disturbance of orientation at the stepped portion in the inside of the pixel causes leaking of light LK thus lowering the display quality. FIG. 13 shows a method which can cope with this lowering of quality. FIG. 13 is a cross-sectional view similar to FIG. 12 and explains a structural example of a transflective liquid crystal display device which possesses the light leaking prevention structure. The structure shown in FIG. 13 prevents the leaking of light by forming such a portion into a non-transmissive portion NT by covering a side surface of the stepped portion with a metal film MT (see JP-A-2002-350840).